Commercial tuna processing remains an essentially manual process in which a multiplicity of individual hand operations are required to separate the edible loin portions of tuna fish from the waste meat and skeletal structure. Such mechanization which has occurred in the industry has been with respect to improved refrigeration, machinery for conveying the fish or its constituents during the processing operation, and machinery for packing the meat into cans.
In the usual processing of tuna for canning purposes, the fish is precooked and is then cooled and routed to work tables for manual manipulation and cleaning. The head and tail are removed and the skin and fins are scraped off, after which the tuna is split longitudinally and the backbone removed. Each half of the split tuna is again longitudinally split to form a pair of discrete dorsal loins (the right and left epaxial muscles), and a pair of discrete ventral loins (the right and left hypaxial muscles). The blood meat and associated dark meat portions are scraped away from the edible loin portions, and the remaining loins, edible flakes and waste products are routed to separate processing stations for further operations to provide respective products. Each of the steps of the processing sequence outlined above is essentially manual in character, and the rate at which the tuna is processed and the quality of the resulting work is quite variable depending upon the skill of the individual worker.
Significantly improved tuna butchering techniques are the subject of U.S. Pat. Nos. 3,593,370 and 3,594,191 of J. M. Lapeyre, and which are assigned to the assignee of the present invention. In the novel methods of the foregoing patents, the tuna is subdivided in its frozen state into a plurality of cross sectional or transverse slices, and the edible loin portions are then separated from the waste meat and bone portions of each slice. The butchering of the tuna is preferably accomplished before any cooking operation. The edible loin portions are cooked separately from the waste products, and as a result, staining of the meat is avoided, thereby improving the yield of canned meat. Such staining of the edible meat can and usually does occur in the conventional processing of tuna, since the entire fish is precooked prior to butchering.
The separation of the edible loin portions in each transverse tuna slice can be accomplished manually or by use of suitably configured dies. The dies are typically of quandrant shape and are sized in accordance with the physical characteristics of the tuna slices, which are usually presorted to provide more uniformly sized slices for cutting at a particular work station. The cutting dies are of fixed size and configuration, while necessarily the edible loins of the tuna slices are of variable aspect. As a result, the edible loin portions are imperfectly separated in that some of the edible meat may not be cut by the die, or the separated loin may include some amount of waste meat.
A butchering technique and means for separation of the edible loin portions of tuna slices from associated waste portions along the actual boundary of the edible loins of slices being butchered, rather than along a boundary presumed for particular slices, is the subject of U.S. Pat. No. 3,800,363, of the same inventor and assignee as herein. In the method and system of U.S. Pat. No. 3,800,363, each -transverse slice of the principal loin bearing section of a tuna is scanned to produce electrical signals representative of the boundary between the edible loin portions and the contigous waste meat portions. Control signals are derived from these electrical signals for control of cutting apparatus for precise separation of the edible loin portions along the detected boundary.
For purposes of this application, the term "tuna" will, because of conventional usage within the boundary, be considered to include the following species of fish: albacore (Germo alalunga), bluefin (Thunnus thynnus), skipjack (Katsuwonus pelamis), yellowfin (Neo-thunnus macropterus), little tuna (Ethynnus alletteratus), Atlantic bonito (Sarda sarda), Pacific bonito (Sarda chiliensis), and yellowtail (Seriola dorsalis).
The individual five species identified immediately above are recognized as species of tuna, the bonito and yellowtail being "tuna-like" fish as they are commercially canned tuna-style, although such canned fish cannot be domestically labeled as "tuna".